A mobile wireless communication scheme is known that assigns one of wireless transmitting/receiving device(s) located on a wireless base station to a call-in or call-out request by a mobile wireless device (see Japanese Patent Application Laid-Open No. 63-180231, for example).
A trunked radio communication system, in which usability of frequency has been improved by sharing a pre-determined number of wireless channels among a plurality of mobile wireless stations using line control apparatuses, is used as a land mobile radio (LMR) system typically for industrial use. In the trunked radio communication system, the wireless base stations located in various places have the line control apparatuses and make the pre-determined number of wireless channels to be sharable among the plurality of mobile wireless stations by transmitting control information to the mobile wireless stations. In this way, by sharing the pre-determined number of wireless channels among the plurality of mobile wireless stations, usability of frequency can be improved compared to a wireless communication system in which each mobile wireless station exclusively uses a dedicated wireless channel.
Generally, in the trunked radio communication system, a single wireless base station manages a plurality of wireless channels, and uses one of the wireless channels as a channel for control (control channel) while it uses the other wireless channels as channels for call (call channels). A mobile wireless station supervises objects received on the control channel, thereby identifies, for example, calling messages sent from the wireless base station on the control channel. If there is calling to the mobile wireless station itself, the station switches to the designated call channel to perform an operation to start a call to, for example, an origin mobile wireless station which made the calling.
More specifically, in North America, while various types of trunked radio communication systems are used, many radio devices on the LTR (Logic Trunked Radio) system are used for simple and low-cost systems. On the other hand, in Japan, the ARIB-T61 system (hereinafter, also referred to as “ARIB” system) is defined as a standard specification.
In a radio communication system on the LTR system, a wireless channel comprises functions applicable for both of control and call, so that a dedicated control channel is not provided. While a wireless channel is not used, the wireless channel is in an idle state due to no transmission on the channel. As soon as a calling mobile wireless station knows that radio wave is not outputted on some of wireless channel bands, it performs processing to transmit a call request message. On the other hand, another mobile wireless station in a wait state cannot predict when a calling message will be sent, so it always stays in a receive state even while no transmission is performed on a wireless channel managed by a wireless base station. When the mobile wireless station receives a calling message from the wireless base station, it extracts identifying information (ID information) in the calling message. If and only if the information matches the identifying information of the mobile wireless station itself, the station switches to the call channel to start a call with the origin mobile wireless station. As above, while the LTR system has an advantage that a link is established between mobile wireless stations as soon as calling is made, it has also a problem that a mobile wireless station in a wait state must always perform a receiving operation.
Further, in a wireless communication system on the ARIB system, for example, one of a plurality of wireless channels managed by a wireless base station is used as a dedicated control channel and is in a transmission state continuously to continue sending control information. The control information sent from the wireless base station on the control channel includes various types of messages including broadcast (notifying) information or calling information. In a wireless communication system on the ARIB system, control information sent on such a control channel has a super frame structure consisting of a plurality of frames so that it is possible to designate which frame in the super frames includes what control information. In this situation, information about the super frame structure is included in broadcast (notifying) information in the control information, so that the mobile wireless station can identify, by receiving the broadcast (notifying) information, in which frame it is called. In frames other than the identified one, for example calling to other mobile wireless stations is made, the mobile wireless stations receive the identified frames only, while it can stop the receiving operation in the other frames.
As described above, in a wireless communication system on the ARIB system, the control information has the super frame structure so that a mobile wireless station can perform intermittent reception. This has an advantage that the operational time can be elongated compared to the case that the receiving operation must be performed continuously. However, since a frame for calling is fixed, the longer the super frame becomes, the longer it takes to establish a link between the mobile wireless stations. Since such a land mobile wireless system provide for, in addition to separate calling to call each mobile wireless station separately, group calling to call a plurality of mobile wireless stations as a group at one time, the mobile wireless station has a function to wait for a plurality of groups simultaneously. This leads to a problem in which it is necessary to check a plurality of frames even in the case of the super frame structure, reducing the advantage of elongating the operational time using the super frame structure.
In a general land mobile wireless system, a user starts a call by switching on (for example, pushing) a PTT (Push-To-Talk) switch. In this system, it is preferred that a time period is as short as possible between the pushing of the PTT switch and start of the call after the completion of the calling process. On the contrary, in a portable mobile wireless station using a battery as power supply, it is preferred to elongate the operational time by reducing consumption current as much as possible, since the consumption current in a wait state shorten the battery life.
The present invention is made in view of the above situation and its object is to provide a wireless communication system, a wireless communication control apparatus, a wireless communication apparatus and a wireless communication method which can start a call in a short time and elongate the operational time.